While there are formulas to figure jetting, I don't even look at the numbers anymore. If you have two of the SAME scoot, and try to jet them exactly the same, one of them will still need to be tweaked. I ran mine for more than a year with what I thought was a good set up, and have since gone up at least 2 sizes on all three jets. I wouldn't even want to try to figure where the difference is. I just started figuring forget the numbers, and look at the plug/ listen to the engine. What I assume happened to dirtyd was he was running rich all along, until he swapped the air filter. Running slightly lean would heat, and dislodge all that carbon on the dome, and valves. In a way it may have been what stopped him from doing any real damage. Once you get it sorted out a little Sea Foam, or OMC Carbon Guard in every tank will keep the carbon out of your engine, and exhaust. Come to think of it, have you done a compression test? Worn rings would be a suspect for abnormal carbon. Same with valve seals.
